1. Field of the Invention
The present invention relates to a crimp-type semiconductor device used for electric power and, more particularly, to a semiconductor device used as the gate turn-off thyristor or transistor whose heat radiation is improved and having non-alloy structure in which electrode members are not soldered to the semiconductor pellet.
2. Description of the Related Art
The structure of the common semiconductor device used for electric power employs a package of the crimp type so as to meet such conditions as heat radiation, current, capacity, explosion-proofness and matching the radius of the semiconductor pellet. One of these crimp-type semiconductor devices is disclosed in U.S. patent application Ser. No. 07/422,900 filed on Oct. 17, 1989 by H. Matsuda et al, for example.
In the case of the GTO thyristor disclosed in the U.S. Patent Application, electrodes on each of both sides of the semiconductor pellet are pressed against an electrode post through an electrode member. The semiconductor pellet is thus uniformly contact-pressed without locally receiving excessive pressing force and stress. More specifically, the outer diameter of the electrode member located on the cathode side of the pellet is made larger than that of the cathode electrode pattern which is opposed to the cathode side electrode member while the inner diameter of the former is made smaller than that of the latter. In addition, the outer diameter of the electrode member located on the anode side of the pellet is made larger than that of the anode electrode pattern which is opposed to the anode side electrode member. Further, the outer diameter of the cathode electrode post is made smaller than that of the electrode member which is opposed to the cathode electrode post. Still further, the outer diameter of the anode electrode post is made smaller than that of the electrode member which is opposed to the anode electrode post.
When the GTO thyristor having the above-described structure is excessively loaded by a particularly high operating frequency or the like at the time of its turn-off, however, positive feedback is caused at that outer rim portion of the semiconductor pellet where heat radiation is not good, in such a manner that power loss is increased to raise the temperature of the pellet and that this process is repeated to further increase the power loss and further raise the temperature of the pellet. As a result, heat break-down is caused at that region of the pellet which vertically crosses the outer rim portion of the pellet.